Check your organic load, Nirates etc. Try to maintain a pH of 8.3 a high pH tends to inhibit the growth of the red cyano. So check your alk maintain it 8-11 dkH. Water flow also plays an important part so make sure there is enough flow in your system. Remember it is a normal part of reef keeping to have out breaks of red slime, every tank has bouts with it especially in newer set ups. Just be pro active and try to siphon it out when you see it. use a small diameter hose so your only taking out a minimum amount of water. 1/2" or 3/8" hose tends to work the best. Good luck.
Keep on reefin'
James